1. Field of the Invention
This invention relates to novel elastomer/oxymethylene polymer blends. This invention further relates to novel elastomer/oxymethylene polymer blends whose impact strength or resistance has been enhanced, with no appreciable diminution in their other useful properties, by the inclusion of a novel elastomer/oxymethylene graft copolymer compatibilizing agent, and relates as well to such compatibilizing agents and processes for their preparation. This invention also relates to molding resins and high performance shaped structures molded therefrom comprising these compatibilized elastomer/oxymethylene polymer blends.
2. Description of the Prior Art
a. Elastomer/Oxymethylene Polymer Blends
Blends of oxymethylene polymers with rubbery polymeric materials are known in the art. For example, U.S. Pat. No. 3,476,832, issued Nov. 4, 1969 to Pritchard and assigned to Celanese Corporation, discloses improving the impact strength and flex resistance of oxymethylene polymers containing at least 60 percent repeating oxymethylene groups by blending them with rubbery polymers, particularly ones having a hydrocarbon backbone and pendant nitrile groups, such as diolefin/acrylonitrile copolymers.
Coupling oxymethylene homo-, co- and terpolymers to other polymers having active hydrogen substituents, such as hydroxyl, amino, amido, carboxyl, mercapto and thiocarbonyl groups, using diisocyanates as the coupling agents, is disclosed in U.S. Pat. No. 3,364,157, issued Jan. 16, 1968 to Halek et al and also assigned to Celanese Corporation.
b. Elastomer/Oxymethylene Graft Polymers
U.S. Pat. No. 3,392,118, issued July 9, 1968 to Isaacson et al, discloses preparing "polymeric formals" which range from viscous liquids to elastomeric solids [molecular weights up to 25,000 (Staudinger)] by condensing a hydroxyl-containing diene polymer, such as a hydroxylated polybutadiene, having a molecular weight of up to about 12,000 (Staudinger) with formaldehyde in the presence of an acid catalyst. Chloroprene is among the typical dienes disclosed by Isaacson et al for use in making their hydroxyl-containing diene polymers. Nonetheless, the entire emphasis in the Isaacson et al patent is on forming oxymethylene graft chains on the hydroxyl-containing diene polymer by reacting formaldehyde with hydroxyl end groups introduced into the diene polymer during peroxide-catalyzed polymerization.
U.S. Pat. No. 4,136,136, issued Jan. 12, 1979 to Dreyfuss et al, discloses grafting polymer chains made up of certain small ring hetero-O, -S or -N compounds from the backbones of halogenated elastomeric polymers under cationic polymerization conditions. Among the small ring monomers disclosed by Dreyfuss et al are cyclic ethers such as tetrahydrofuran, cyclic formals such as 1,3-dioxolane and cyclic epoxides such as propylene oxide, while the halogenated elastomeric backbone polymers disclosed include chlorinated butadiene, chlorinated SBR, PVC, chlorinated EPR, chlorinated EPDM, neoprene and chlorobutyl rubber. And Dreyfuss et al disclose that silver salt catalysts are particularly useful in carrying out their graft polymerizations; see also Dreyfuss et al, J. Polymer Sci.: Symposium No. 56, 129-137 (1976). It has now been determined experimentally, however, that trioxane, another small ring hetero-0 monomer (and one commonly employed, together with cyclic ethers, formals, etc. having at least two adjacent carbon atoms, to prepare oxymethylene copolymers), will not react under cationic polymerization conditions such as those disclosed in the Dreyfuss et al patent and article to graft polyformaldehyde [poly(oxymethylene)] chains onto halogenated elastomer backbones.
Soluble copolymers of tetrahydrofuran grafted onto Neoprene W, prepared in the presence of nitrosyl and nitryl hexafluorophosphates, are disclosed by Eckstein et al in J. Polym. Sci.; Polym. Chem. Ed., 17, 4115-4121 (1979).
U.S. Pat. Nos. 3,555,121, issued Jan. 12, 1971 to Tanaka et al and 3,872,182, issued Mar. 18, 1975 to Sextro et al, disclose grafting trioxane-cylic ether or -cyclic acetal chains onto various unhalogenated polymer backbones, including backbones having pendant alcohol ester or acid ester groups which act as grafting sites, under cationic polymerization conditions.
None of the aforementioned literature articles and patents teach the grafting of polyformaldehyde [poly(oxymethylene)] or oxymethylene copolymer chains onto halogenated diene polymer backbones or the use of such graft polymers as compatibilizing agents for elastomer/oxymethylene polymer blends.